1. Field of the Invention
This invention generally relates to valving apparatus useful in a drill string application and more specifically to apparatus that is useful for including in a kelly saver subassembly to substantially reduce mud spills therefrom.
2. Description of the Prior Art
The kelly along with the kelly bushing provides a long spline used in a drilling rig operation as that portion of the assembly that permits connection of new drill pipe joints to the string or stem as the drilled bore hole becomes deeper. For a typically length hole of 12,000 feet, there are approximately 400 connections of 30 foot long pipe that must be made by the kelly or the kelly assembly.
The bore of the kelly, during drilling operation, also accepts drilling fluid or mud on the way from the mud reservoir to the drill string. When it is necessary to "break" the string at the kelly, the pressurizing pump is turned off and the string is disconnected at the kelly for the purpose of either adding a joint of drill pipe as drilling progresses. Each time the kelly is disconnected when it has mud present in its bore, about one-half barrel of the mud is spilled. To prevent this from happening, manual valve closures have been employed. In addition, a somewhat complex automatic device called a kelly foot valve has been developed, which is the subject of U.S. Pat. No. 3,698,411. This device operates satisfactorily, but is longer, more costly and more difficult to maintain than the device described hereinafter.
Generally, a kelly mud saver valve should accomplish the functions described hereinafter. First, as mentioned above, the valve must prevent mud from being released from the bore of the kelly when the lower connection is unscrewed to add another joint or length of drill stem. The pressure of the mud weight due to the hydrostatic head may be up to approximately 100 pounds per square inch and the valve must seal against this pressure to retain the fluid.
When the joint of drill stem is added and drilling operation commences, the primary circulating pump is turned on. Therefore, secondly, the valve must fully open when subjected to a higher pressure than the nominal pressure described above and it must stay open during normal fluid flow so as not to create a substantial pressure drop across the valve.
Third, the valve must not seal against back pressure when the drill stem is all connected together and the stem is pressurized. This is necessary so the pressure gauge on the stand pipe will always indicate if there is any pressure on the threaded connection that is to be unscrewed to add another length of pipe. Unscrewing a threaded connection under pressure is potentially very dangerous. In some conditions where back pressure is occurring, it may be necessary to flow a large volume of fluid upward through the valve; therefore, the valve must remain open under these conditions.
Finally, it is necessary to be able to run a wire line tool through the valve in emergency situations. Therefore, the closure mechanism in the bore must be removable or readily destructable to permit such operation.
The device that is hereafter described performs all of the above functions.
It is therefore a feature of the present invention to provide an improved mud saver valve for automatically substantially preventing mud spills from a kelly assembly, while otherwise permitting ordinary mud operation therethrough.